1. Field of the Invention
The present invention relates to vapor deposition method and apparatus and, more specifically, to vapor deposition method and apparatus suitable for forming an organic material layer configuring an organic electroluminescence element.
2. Description of the Related Art
In an organic electroluminescence (hereinafter, organic EL) display device, organic EL elements to be driven by current are two-dimensionally arranged for image display. The organic EL elements are each generally configured by an insulator substrate formed thereon with a pair of electrodes. The substrate is made of glass, for example, and is exemplified by an active substrate formed thereon with a thin-film transistor or others for pixel driving. On one of the pair of electrodes, organic material thin films, i.e., organic films, are formed in order. The organic material thin films include a hole-injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron-injection layer, and over the top layer of the resulting laminate structure, an electrode film of the remaining electrode is formed. Above such an electrode film of the remaining electrode, an encapsulation substrate is provided for protecting the organic EL elements from the external atmosphere, and preventing moisture or others from entering thereinto. The encapsulation substrate is also referred to as encapsulation cap.
By the pair of electrodes formed with such a laminate structure sandwiching therebetween, a flow of current is directed in the layer-laminated direction of the laminate structure. At least one of the pair of electrodes is configured by a transparent electrode in a so-called bottom emission type. The transparent electrode easily passes through visible light, and emits display light to the side of the active substrate. Needless to say, but the encapsulation substrate is also a transparent substrate.
More specifically, a glass- or plastic-made transparent substrate is formed thereon with one of a pair of electrodes provided to every pixel, i.e., first electrode (generally anode electrode). On the first electrode, various layers are laminated in order so that an emission layer is configured. The various layers include a hole-injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron-injection layer. After such layer lamination, the electron-injection layer, i.e., the top layer of the resulting laminate structure, is covered by the remaining electrode, i.e., second electrode (generally cathode electrode), thereby a flow of current is directed between the first and second electrodes. With the flow of current, carriers (electrons and positive holes) having been injected into the laminate structure, i.e., emission layer, are coupled again so that light is emitted. If with a so-called top emission type with which display light is directed in a direction opposite to the encapsulation substrate, the first electrode may be a reflecting electrode made of a metal film, and the active substrate may not also be necessarily transparent. Note that, in the below, the active substrate is simply referred to as substrate unless otherwise required.
An organic film is generally formed by vacuum vapor deposition method. The organic material layers configuring the laminate structure formed on the substrate as such are each formed by evaporating an organic material on the main surface of a substrate placed in a vacuum chamber. Before such material evaporation, the organic material is heated, for vaporization, up to the vaporization temperature or closer in an evaporation crucible of an evaporation source unit, which is disposed in the vacuum chamber in a vacuum atmosphere. More in detail, on the main surface of a substrate placed in a vacuum chamber, a metal-made mask (so-called metal mask) is disposed with an aperture pattern corresponding to the pixel arrangement on the main surface.
Through the aperture of the mask, the vaporized organic material is evaporated on a specific area of the main surface of the substrate, e.g., portion corresponding to each pixel, so that the organic material is evaporated thereon in the form of a thin film. Herein, for evaporation of the emission layer described above, a main material, i.e., an organic material, may be evaporated on the specific area of the main surface of the substrate together with an additive material e.g., organic material of another type, at the same time.
The metal mask is attached or welded to a mask frame, i.e., metal-made frame, with tension applied for keeping flat the plane thereof. In the below, the combination of the metal mask and the mask frame is referred to as evaporation mask.
The evaporation crucible is provided with a vaporizer vessel for storing therein an organic material. The organic material stored in the vaporizer vessel is vaporized so that an evaporation film of the organic compound is formed on the substrate placed in the vacuum chamber. This vaporizer vessel is provided with an exhaust nozzle, i.e., nozzle portion, for use to control the direction and amount of the vaporized organic material dispersing into the vacuum chamber.
Generally, the vacuum vapor evaporation method is mainly classified into two systems, i.e., cluster system and in-line system. Patent Document 1 (JP-A-2006-260939) describes the cluster system in which a vacuum chamber, i.e., transfer chamber, is disposed at the center for transfer use, and another vacuum chamber (processing chamber) is disposed therearound for film formation use. The transfer chamber at the center is provided therein with a robot, and transfers only substrates one by one. Thus transferred substrates are each heated first in a heating chamber, and the heated substrate is then transferred to an oxygen plasma processing chamber for surface conditioning. After cooling the substrate in a cooling chamber, the substrate is transferred to another cluster device for a process of film formation.
For film formation, in the processing chambers, an evaporation mask and a substrate are made ready for each thereof, and are aligned and overlaid one on the other before film formation. In Patent Document 1, the substrates are cooled in advance before film formation as such so that any misalignment possibly caused by thermal expansion of the substrates has been prevented. For film formation, two methods have been in practical use, i.e., forming a film by scanning an evaporation source with the substrate side fixed, and fixing an evaporation source with the substrate side fixed.
Patent Document 2 (JP-A-2002-348659 and its counterpart United States Patent Application Publication No. US 2002-0179013 A1) describes the in-line system in which processing chambers are disposed in order of a process of film formation, and a combined structure of an evaporation mask and a substrate overlaid one on the other is fixed to a carrier. The resulting carrier is transferred by a transfer roller disposed in each of the processing chambers. The processing chambers are each provided with a fixed evaporation source, and film formation is carried out by the carrier passing in the front of the evaporation source.
In the cluster system, a substrate is transferred between a transfer chamber and a processing chamber, and after such a substrate transfer, the substrate is required to be aligned with an evaporation mask in each of the processing chambers. In consideration thereof, for processing substrates in a sequential manner, the in-line system leads to better efficiency in terms of throughput and the use of material.
On the other hand, with vacuum vapor evaporation, there is a problem when films are formed differently on the basis of pixel, i.e., both a substrate and an evaporation mask are increased in temperature, thereby causing misalignment due to thermal expansion. Patent Document 3 (JP-A-2004-214185) proposes a method of reducing such a temperature increase of a substrate and an evaporation mask with a structure in which a crucible opposing a substrate is formed with a portion protruding toward the substrate, and the protrusion portion is formed with a hole for discharge of steam, thereby preventing any possible radiant heat around the protrusion portion.